Raids bring Rets for the utility, not the damage. Their damage is going to be sub-par until Naxx, and there is no way around it.
The utility that a Ret brings is what makes them viable. Unlike HPalas, Rets do not need to stop casting in order to perform tasks like Cleansing, BoPing, Lay on Hands for the Tank, or throwing a Blessing on a target if the died and were battle res'd. Rets also have an easier time keeping Blessing of Sacrifice up on a tank, redirecting 55 damage from every hit to themselves. As for Lay on Hands, Ret Paladins do need their mana to dps effectively, but their mana is much less important to them than it is to a Holy Paladin. Ret Paladins also have the benefit of being glued to the boss, where they can effectively regen mana from Judgement of Wisdom. Rets can also be your designated Nightfall bot, and are very effective at doing so. In addition, a Ret Paladin can still throw on a dress and heal relatively effectively. They won't beat true Holy Paladins, of course, but the ability to switch to healing depending on encounter is extremely valuable, and is something that no other melee DPS can do (Ferals *can*, but are much less effective at doing so).
So if anyone tells you that Ret DPS isn't viable, they are both right and wrong. In terms of raw DPS, a Ret Paladin is not viable. However, in terms of raid utility, Ret DPS is extremely viable. If your raid does not need the extra utility that a Ret Paladin brings, then they are not viable. If your raid could use the extra utility, then yes, a Ret Paladin will be extremely valuable.
Keep in mind that if you are to be useful to your raid, you can't just sit and tunnel the boss like Rogues and Warriors. You have to keep an eye open and use your utility to your raids advantage. If you don't do this, you are dead weight to your raid. Unfortunately, 95% of Ret Paladins on this server forget this fact, and play as if they were a Warrior. This gives Ret Paladins a bad reputation, which will make it difficult to convince raids to take you.
What I would do if I were you is I would stick it out as Holy until the AQ release. Let your raid leader know that you are extremely interested in going Ret, and let them know about the utility that a Ret Paladin brings. Also volunteer to be a Nightfall bot if your raid doesn't have one. Even then, it's not a bad thing to have more than 1 Nightfall bot, but 1 is usually enough if your offtanks all also have one.
It's also good to mention that AQ and Naxx are when Ret DPS finally hits its stride. Blizzard finally releases gear with STR, SP, and Melee Crit with T2.5 for Paladins, which drops in AQ, which remains as BiS through Naxx. The release of Naxx also allows us access to DPS spells like Exorcism and Holy Wrath, which is another bonus to our DPS, especially given the SP gear we got out of AQ. In Naxx, Ret DPS isn't competitive with Warriors obviously, but becomes competitive with most DPS classes. Check out the infamous Esotarious video here:
https://www.youtube.com/watch?v=VEs9coe5XRgIt's also worth mentioning that Esotarious wasn't playing optimally. He was using an Axe, which means he missed out on the human racial of +5 swords and maces, and didn't have Consecrate specced, which is a huge DPS loss. He also was not using HoJ, and did not have Libram of Fervor equipped. He was also under the hit cap by 2%. Again, this doesn't mean much now since Naxx is a long way away, but it's still worth mentioning that in retail vanilla a Ret Paladin was competitive in terms of DPS in Naxx despite not playing optimally.
